A virtual image displaying device (image displaying device) used for allowing an observer to observe a two-dimensional image formed by an image forming device as a magnified virtual image by using a virtual image optical system is known, for example, as in JP-A-2006-162767.
The image displaying device 100, as illustrated in FIG. 1 as a conceptual diagram thereof, includes: an image forming device 111 that includes a plurality of pixels arranged in a two-dimensional matrix pattern; a collimator optical system 112 that makes light emitted from the pixels of the image forming device 111 to be parallel light; and an optical device (light guiding unit) 120 to which the light formed as the parallel light by the collimator optical system 112 is incident, through which the incident light is guided, and from which the guided light is output. The optical device 120 is configured by: a light guiding plate 121 allowing the incident light to propagate the inside thereof through total reflection and output therefrom; a first deflection unit 130 (for example, configured by a single-layer light reflecting film) reflecting the light incident to the light guiding plate 121 such that the light incident to the light guiding plate 121 is totally reflected inside the light guiding plate 121; and a second defection unit 140 (for example, configured by a multi-layer light reflecting film having a multilayered stacked structure) allowing the light that has propagated the inside of the light guiding plate 121 through total reflection to output from the light guiding plate 121. For example, by configuring an HMD by using the above-described image displaying device 100, a miniaturized, lightweight device can be realized.
In addition, in order to allow an observer to observe a two-dimensional image formed by an image forming device as a magnified virtual image through a virtual image optical system, a virtual image displaying device (image displaying device) using a hologram diffraction grating is known, for example, as in JP-A-2007-94175.
The image displaying device 300, as illustrated in FIGS. 20A and 20B as a conceptual diagram thereof, basically includes: an image forming device 111 that displays an image; a collimator optical system 112, and an optical device (light guiding unit) 320 to which light displayed in the image forming device 111 is incident and which guides the light to the pupils 21 of the observer. Here, the optical device 320 includes a light guiding plate 321 and a first diffraction grating member 330 and a second diffraction grating member 340 each configured by a reflection-type volume hologram diffraction grating arranged on the light guiding plate 321. To the collimator optical system 112, light emitted from each pixel of the image forming device 111 is incident, and parallel light is generated by the collimator optical system 112 and is incident to the light guiding plate 321. The parallel light is incident from the first face 322 of the light guiding plate 321 and is output. Meanwhile, the first diffraction grating member 330 and the second diffraction grating member 340 are attached to the second face 323 of the light guiding plate 321 that is parallel to the first face 322 of the light guiding plate 321.
Through a head-mounted display having a see-through function, a virtual image of an image displayed by an image displaying device can be observed while viewing a real image in a real space disposed in front of the eyes. Accordingly, such a type of display is expected to be used for an application as navigation for an airplane including a helicopter and the like and in part this has been put into practice. Generally, in a transportation unit such as an airplane that is expected to move at a relatively high speed, an operator frequently looks at a position located at an infinite distance in a real space. Thus, when the virtual image distance of an image displayed by a head-mounted display having a see-through function that is used for an application of the navigation of an airplane or the like is set to infinite, in other words, when the convergence angle is set to zero, or when the main light beams transmitted from two image displaying devices for the left and right eyes are set to be parallel to each other, a reduction in visibility due to a distance difference between a real image and a virtual image can be substantially resolved.